The invention relates to a seal arrangement for a shaft having a broad rpm range, supported in a housing, in particular for axle drives.
For the sealing of shafts, a multiplicity of seals are often used, which are primarily intended to protect the shaft bearing or the axle drive from loss of lubricant and, in addition, to prevent contaminants from penetrating into the shaft bearing arrangement.
Among the seal arrangements that are often used are radial shaft seals, which are inserted into the housing bore hole and contact the periphery of the shaft at a flexible lip seal. However, these seals are less suited for axle drive seals because they prevent the penetration of contaminants only to a limited extent. The arrangement of one or a plurality of additional radial protective lips is also not completely satisfactory.
Consequently, so-called cassette seals have begun to be used, in which a sleeve is placed on the shaft and is provided with a radial flange as a baffle plate. The primary lip seal, which contacts the circumferential surface of the sleeve at the sealing lip, is provided with a protective lip which comes into contact with the radial flange. The axially oriented protective lip is to prevent the penetration of contaminants. In addition, as soon as the shaft begins to rotate, contaminants, dust, and also water that has found its way in are expelled by the radial flange, which represents a baffle plate.
All of the heretofore known embodiments have in common that the radial or also axial protective lips heat up intensely in response to high rotational speeds and are subjected to excessive wear. As a result, the effectiveness and service life of the seals are reduced.
The invention is directed to the task of creating a seal arrangement which provides as reliable a seal as possible and is, in particular, little subject to wear. A seal arrangement is configured and is provided, in particular, for axle drives. However, if necessary it can also be used in other locations if the shafts are subject to the threat of soiling at rest and in the entire rpm range. The seal arrangement is therefore generally suitable for shafts having a broad rpm range. The seal, arranged in the housing bore hole for sealing off the shaft bearing space from loss of lubricant, and a baffle plate, joined to the shaft and having, oriented radially towards the inside, a lip seal which under the effect of centrifugal force lifts off from its sealing surface in response to increasing rotational speeds of the shaft. The material for the lip seal is selected so that the lip seal, when the shaft is at rest or rotating at relatively slow speeds, sealingly contacts the sealing surface assigned to it as a result of its internal tension. The lip seal is joined to the baffle plate and, at higher rotational speeds, widens, with the consequence that the sealing lips separate from the sealing surface. As a result, unnecessary friction between the sealing lips and the sealing surface is avoided, and a heating of the sealing lips does not take place.
The radial shaft seal in its fundamental design is composed of an external holding part, inserted into the housing bore hole in a press fit, and an interior lip part, supporting the primary sealing lip for the shaft. The holding part is preferably provided with a reinforcing ring, which is at least partially covered by an elastic polymer packing. The primary sealing lip of the lip part can be encircled by a wire filament spring (all well-known components).
The baffle plate, cooperating with the seal, is secured on a shaft shoulder via a sleeve or the like. At its external edge, the baffle plate has an exterior ring that is aligned with the radial shaft seal, the interior edge of the exterior ring producing a labyrinth seal in cooperation with the polymer packing of the holding part. It is expedient if this labyrinth seal is formed by a gap, aligned axially and radially, between a protruding ring bead of the holding part and a right-angle bend at the interior edge of the exterior ring, aligned radially to the outside and resting inside the ring bead. On the holding part of the radial shaft seal, therefore, a ring bead protruding to the outside is present, which overlaps the interior end of the exterior ring secured on the baffle plate. Between the holding part having the ring bead and the right-angle bend of the exterior ring, a labyrinth gap is therefore formed. The exterior ring of the baffle plate is preferably enclosed by a polymer, which at the interior edge of the exterior ring can replace the right-angle bend through a corresponding configuration.
According to one advantageous aspect of an embodiment of the invention, the lip seal is integrally connected to the polymer of the exterior ring. This connection is configured and arranged so that the connection permits a rotating motion (a lifting off) of the lip seal, beginning at a predetermined shaft rotational speed. For example, this can be achieved through because the connection is composed of a conical tapering of the lip seal as it approaches the connecting point. In general, the design of the lip seal can be compared to a conventional sealing lip. However, it is advantageous if the lip seal is provided with two protective lips or sealing edges, in order, in every case, to prevent the penetration of contaminants, particularly water.
The sealing surface for the lip seal is formed by a metal slide sleeve that is aligned co-axially with respect to the shaft and is joined to the lip part of the radial shaft seal. This slide sleeve on its interior surface can at least partially be lined with the polymer material of the lip part. It is expedient to provide it with two radial protective lips to strengthen the barrier against contaminants.
The seal arrangement according to the present invention is particularly suited for axle drives and transfer cases of so-called off-road vehicles. It reliably prevents the penetration of contaminants and also water when the shaft is at rest or rotating at lower speeds, as a result of the fact that the lip seal prevents the penetration of water. The labyrinth seal also contributes in this respect due to the fact that it considerably reduces the pressure of the inflowing water. As the rotational speed of the shaft increases, the baffle plate and also the right-angle bend at the end of the exterior ring of the baffle plate more and more take effect, until finally neither contaminants nor fluids can penetrate into the interior of the seal. In response to the increasing rotational speeds of the baffle plate, the lip seal begins to widen, or to rotate about its connecting point, so that the sealing lips lift off from the sealing surface of the slide sleeve. In this context, the sealing lips are supported on the interior circumference of the exterior ring. The friction between the lip seal and the slide sleeve is therefore eliminated.
Within the framework of the conception of the invention, other configurations of course are also conceivable, it being possible, for example, that the exterior ring of the baffle plate is configured conically having a radius that increases to the interior of the radial shaft seal. Also possible are other configurations of the lip seal or of the slide sleeve.